1. Field of the Invention
The invention pertains to control of synchronous stepper motors. More particularly, the invention concerns a microprocessor-based controller for a stepper motor driven machine tool size adjusting system.
2. Description of the Prior Art
The process of automatic tool compensation in machining is known wherein a cutting edge such as on an indexable carbide insert is adjusted relative to a workpiece to compensate for tool wear. As an added feature, such a compensator can advance the tool prior to beginning a cut and retract the tool a distance from the workpiece surface prior to the retract machine stroke so as to avoid drag-out marks on the surface of the workpiece when the machining process is finished.
One known compensation arrangement utilizes a stepper motor to control compensation either by positioning a stop for an hydraulically driven piston or to directly control insert position via a stepper motor drive translator and ball screw module. Such arrangements are taught in U.S. Pat. No. 3,740,161, issued June 19, 1973, and assigned to the same assignee as the instant invention.
The stepper motor is a specialized form of a synchronous machine designed to rotate its rotor a predetermined amount in response to each electrical pulse received by its drive unit. The rotation is effected by delivering appropriate currents to sequentially selected stator windings of the motor to force the axis of the air gap between rotor and stator poles into alignment.
Prior art stepper motor controllers for furnishing desired motor drive pulse commands have typically been constructed with a large plurality of fixed RC networks in a voltage-controlled oscillator for synthesizing a desired motor velocity versus time waveform. Motor velocity versus time acceleration/deceleration waveforms generated in such a discrete fixed manner have typically been poor approximations of idealized maximum motor performance characteristics and have been difficult to "fine tune".